著者

TOMO TAKANO MASATO NAKATSUKASA MARTA PINA YUTAKA KUNIMATSU YOSHIHIKO NAKANO NAOKI MORIMOTO NAOMICHI OGIHARA HIDEMI ISHIDA

出版者

The Anthropological Society of Nippon

雑誌

Anthropological Science (ISSN:09187960)

巻号頁・発行日

pp.200116, (Released:2020-03-17)

被引用文献数

4

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This article reports eight new humeral, ulnar, and radial fragments of Nacholapithecus kerioi collected from Nachola, Kenya during the 1998/1999 field seasons. The study refines the description of its forelimb bones, which was mostly based on a single partial skeleton. The most distinctive feature of the distal humerus is a large, globular, medially tilted capitulum. The groove between the capitulum and the zona conoidea is quite deep. The medial part of the humeral trochlea is also diagnostic in showing a less salient medial border. The medial epicondyle is moderately long and more posteriorly reflected than was previously presumed. The coronoid process of the ulna is quite wide. Its medial portion is distinctly concave. The ulnar shaft is anteroposteriorly deep in its proximal half, slender, straight in frontal view, and weakly anteriorly bowing. The elbow of Nacholapithecus exhibits a primitive functional pattern as a hominoid, including lack of universal stability of the humeroulnar joint through full extension and flexion, restriction of hyperextension of the elbow, and relatively anteroposteriorly oriented loading at the proximal ulna. On the other hand, it is derived in terms of enhanced rotational mobility and stability of the radius, incipiently increased stability at the humeroulnar joint, and more frequent maximum extension of the elbow compared to proconsulids. This mosaic morphology is different from both early Miocene proconsulids and later suspensory or orthograde European fossil apes. Although Nacholapithecus was neither suspensory nor orthograde, its forelimbs may have played a greater role for body support or balance maintenance, more frequently reaching to and exploiting overhead supports than in early Miocene proconsulids.

著者

YUTAKA KUNIMATSU HIROSHI TSUJIKAWA MASATO NAKATSUKASA DAISUKE SHIMIZU NAOMICHI OGIHARA YASUHIRO KIKUCHI YOSHIHIKO NAKANO TOMO TAKANO NAOKI MORIMOTO HIDEMI ISHIDA

出版者

The Anthropological Society of Nippon

雑誌

Anthropological Science (ISSN:09187960)

巻号頁・発行日

vol.125, no.2, pp.59-65, 2017 (Released:2017-09-21)

参考文献数

52

被引用文献数

2

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We here describe a prosimian specimen discovered from the early Middle Miocene (~15 Ma) of Nachola, northern Kenya. It is a right maxilla that preserves P4–M3, and is assigned to a new species of the Miocene lorisid genus Mioeuoticus. Previously, Mioeuoticus was known from the Early Miocene of East Africa. The Nachola specimen is therefore the first discovery of this genus from the Middle Miocene. The presence of a new lorisid species in the Nachola fauna indicates a forested paleoenvironment for this locality, consistent with previously known evidence including the abundance of large-bodied hominoid fossils (Nacholapithecus kerioi), the dominance of browsers among the herbivore fauna, and the presence of plenty of petrified wood.

著者

MASATO NAKATSUKASA NAOKI MORIMOTO TAKESHI NISHIMURA

出版者

The Anthropological Society of Nippon

雑誌

Anthropological Science (ISSN:09187960)

巻号頁・発行日

pp.190908, (Released:2019-10-12)

被引用文献数

1

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Sesamoids of the metacarpophalangeal joint are tiny bones located in the volar plate and articulated with the metacarpal head. Almost all living humans have radial and ulnar sesamoids in their pollical metacarpophalangeal joints. These bones protect and guide the tendon of the long (= extrinsic) pollical flexor. Whereas this condition is considered to be primitive for primates, living great apes have a tendency to lose these pollical sesamoids. Susman (Science 1994; 265: 1570–1573) correlated the loss of the pollical sesamoids in living great apes with the remarkable reduction/loss of the tendon of the long pollical flexor. However, the prevalence of these pollical sesamoids in chimpanzees drastically differs among previous studies. Thus, we CT-scanned cadavers of 12 chimpanzees, four gorillas, and two orangutans, and investigated the frequency of pollical metacarpophalangeal joint sesamoids in these apes. Combining our findings with previously reported data gave updated frequencies of 21% in chimpanzees (n = 24) and 0% in gorillas (n = 7) and orangutans (n = 6). This result is in accordance with the purported independent reduction (or loss) of the tendon of extrinsic flexor of the pollex in great apes (Diogo et al., Journal of Human Evolution 2012; 63: 64–78) and underscores the view that living great apes independently lost this tendon–sesamoid complex. Given that a reduction (or loss) of the tendon of extrinsic pollical flexor in great apes is a trade-off between emphasis on hook grips and pollical reduction, human hands have not experienced specialization for hook grips and retain the primitive condition in this regard. Orangutans and chimpanzees independently specialized for hook grips. The case for gorillas, whose hand proportion is similar to that of humans, is equivocal. Gorilla hands may have attained their current state secondarily or they may have lost the powerful extrinsic flexor of the pollex for reasons other than specialized hook grips.